Why is my body not storing vitamin D? Unlocking the complex causes of low levels

October 14, 2025 •

3 min read

According to research, up to 60% of nursing home residents and 57% of hospitalized patients in the U.S. have been found to be vitamin D deficient, highlighting a widespread issue. But for many, the challenge goes beyond simple sun exposure, with complex factors dictating why is my body not storing vitamin D effectively.

Quick Summary

Examines the underlying medical and lifestyle reasons for poor vitamin D storage, such as malabsorption, chronic illness, medication side effects, and obesity. Outlines how the body processes vitamin D and provides actionable steps for improvement.

Key Points

Malabsorption is a primary cause: Digestive conditions like celiac or Crohn's prevent proper vitamin D absorption in the gut.
Obesity traps vitamin D: High body fat can sequester the vitamin, making it less available for use by the body.
Organ health is critical: The liver and kidneys must function correctly to convert vitamin D into its active and storage forms.
Medications can interfere: Certain drugs, including some anti-seizure medications and steroids, speed up the metabolism or hinder absorption of vitamin D.
Underlying causes require medical intervention: Effective treatment often involves more than just sun or supplements, necessitating a doctor's diagnosis and specific medical management.
Fat is essential for absorption: Because vitamin D is fat-soluble, dietary fat is required for the body to absorb it from food or supplements.

The Journey of Vitamin D: From Source to Storage

Before delving into why your body might not be storing vitamin D effectively, it's helpful to understand how it's processed. Vitamin D exists in two primary forms, D2 and D3, both inactive until they are metabolized by the body.

Sources: Vitamin D is obtained from sun exposure, diet, and supplements.
Liver Conversion: In the liver, vitamin D is converted into 25-hydroxyvitamin D, the main storage form. This is what is typically measured in blood tests to assess vitamin D status.
Kidney Activation: The kidneys then convert 25-hydroxyvitamin D into the active hormone, 1,25-dihydroxyvitamin D.
Storage: The storage form (25-hydroxyvitamin D) is primarily held in fat cells. Issues at any point in this pathway can lead to low levels.

Why Your Body Fails to Absorb and Store Vitamin D

Low vitamin D levels often stem from multiple factors rather than a single cause. If you have low levels despite sufficient intake, one or more of these issues could be contributing.

Malabsorption Disorders: The Gut Barrier

As a fat-soluble vitamin, vitamin D requires dietary fat for proper absorption in the small intestine. Conditions that impair fat absorption can significantly reduce the body's ability to absorb vitamin D from food and supplements. These include:

Celiac Disease
Crohn’s Disease and Ulcerative Colitis
Cystic Fibrosis
Bariatric surgery, like gastric bypass, also reduces the absorptive surface area.

Obesity: Sequestration in Fat Tissue

Fat tissue stores vitamin D. However, in individuals with obesity, excess body fat can sequester the vitamin, reducing its circulation in the bloodstream and its bioavailability. This often necessitates higher supplement doses to achieve adequate levels.

Liver and Kidney Dysfunction

The conversion of vitamin D into its active form relies on healthy liver and kidney function.

Chronic Liver Disease: Can impair the liver's initial conversion of vitamin D to its storage form.
Chronic Kidney Disease: Hinders the kidneys' ability to convert the storage form into the active hormone needed for calcium absorption.

Medications That Interfere with Vitamin D

Certain medications can affect vitamin D metabolism by increasing its breakdown or blocking absorption. Examples include:

Anti-seizure drugs (e.g., phenytoin)
Steroids (e.g., prednisone)
Weight-loss medications (e.g., orlistat)
Cholesterol-lowering drugs (e.g., cholestyramine)

Insufficient Exposure to Sunlight

While not a storage issue, inadequate sun exposure is a prevalent cause of deficiency. Factors contributing to insufficient sun exposure include living at northern latitudes, spending limited time outdoors, having darker skin, and using sunscreen.

Comparison of High-Risk Factors vs. Supporting Strategies


High-Risk Factor	Why it Affects Vitamin D	Supporting Strategies
Malabsorption	Conditions like Crohn's, celiac disease, or bariatric surgery damage the intestine, hindering fat and nutrient absorption.	Target the underlying condition; use high-dose, doctor-supervised supplementation.
Obesity	Excess fat tissue sequesters vitamin D, limiting its bioavailability in the bloodstream.	Requires larger doses of supplements to raise circulating levels. Regular activity can also help.
Chronic Liver Disease	The liver's ability to convert vitamin D into its storage form is compromised.	Supplement with higher doses of vitamin D under a doctor's care. Address the underlying liver condition.
Chronic Kidney Disease	Kidneys are unable to convert the storage form into the active, usable form.	Close medical management of kidney disease is essential. Active vitamin D analogs might be prescribed.
Medication Use	Certain drugs like steroids or anti-seizure medications accelerate vitamin D breakdown.	Consult a doctor about potential drug interactions; adjust medication or supplement dosage as advised.

Conclusion

Persistent low vitamin D levels may require more than just increased sun exposure or standard supplements due to the complex processes involved in its absorption, conversion, and storage. Medical conditions, medications, and lifestyle factors can disrupt this process. Identifying the root causes with a healthcare provider allows for a targeted approach, which may include treating underlying conditions, adjusting medications, or using tailored supplementation to improve vitamin D levels and ensure optimal health.

For further reading on nutrient absorption, the National Institutes of Health offers comprehensive resources on fat-soluble vitamins.

Frequently Asked Questions

Medical conditions that cause malabsorption include celiac disease, Crohn's disease, cystic fibrosis, and liver or kidney disease. Weight-loss surgeries like gastric bypass can also impair absorption.

Obesity can cause low vitamin D levels because the vitamin is fat-soluble and gets stored in excess fat tissue. This sequestration makes it less available to circulate in the bloodstream.

Yes, chronic liver disease can significantly impair the liver's ability to perform the first necessary conversion step of vitamin D, leading to a deficiency in the storage form.

The kidneys perform the final conversion of vitamin D into its active form. Chronic kidney disease can disrupt this process, affecting both circulating levels and the body's ability to effectively use the vitamin.

Medications that interfere with vitamin D include certain anti-seizure drugs (e.g., phenytoin), steroids (e.g., prednisone), weight-loss drugs (e.g., orlistat), and some cholesterol-lowering drugs.

No, while inadequate sun exposure is a common cause, it's not the only one. Other significant factors include malabsorption issues, obesity, chronic liver or kidney disease, and the use of certain medications.

For malabsorption disorders, it's crucial to address the underlying medical condition. A doctor may also recommend high-dose supplements, often of vitamin D3, taken with a meal containing fat to maximize absorption.